This invention relates to improvements in an elevator control system utilizing a thyristor type Ward-Leonard system.
In order to control elevator systems, there has been recently adopted the so-called thyristor type Ward-Leonard system in which the direct current motor for driving an elevator car is controlled by a thyristor device rather than by a conventional motor-generator unit. It is well known that, with the thyristor type Ward-Leonard system the armature current of the direct current motors for operating elevator cars include a multitude of ripples. Those ripples have a fundamental frequency generally equal to six times the frequency of the alternating current from an associated source of electric power. The flow of such a ripple current through the armature of the motor results in the generation of discordant electromagnetic noise from the motor. This noise should be as low as possible in equipment such as elevator systems installed within general buildings.
In order to reduce such noise, it has been previously known to connect a large-sized direct current reactor in the circuit with the direct current motors. If it is attempted in this way to reduce the noise to a level practically allowable by providing the direct current reactor, then the reactor is required to be fairly large-sized which inevitably becomes uneconomical.
Accordingly it is an object of the present invention to provide a new and improved elevator control system utilizing a static Ward-Leonard system and having a reduced amount of noise generated from the direct current motor involved due to the presence of the static Ward-Leonard system.